It is often desirable to generate an artificial shadow for an image. Conventionally, one of two methods are often employed to generate an artificial shadow for an object.
Using the first method, the following three steps may be performed:
a. a control file is generated indicating the border or contours of the desired shadow area and the border or contour of the object. This step may be carried out using the MASK function on the Prisma workstation, commercially available from Scitex Corporation. PA0 b. A degrade' or vignette is generated in a separate file according to the contour defined by the control file. The step may be carried out using the INTERACTIVE CT CREATE function on the Prisma workstation. Typically, a dark color value is selected for the border of the shadow contour which is intended to be adjacent to the object and a light color value is selected for the portion of the border of the shadow contour which is not intended to be adjacent to the object. PA0 c. Finally, the degrade' file and the file containing the original object are merged into a single file.
The second method involves use of an airbrush to draw the shadow by hand. This method requires considerable artistic ability and coordination.
A third method employs a function called TPVN (two-point vignette) on Scitex's Imager workstation. The method is generally similar to the airbrush method in that artistic ability and coordination are required. The TPVN function allows a user to manually manipulate a vignette with two adjustable ends.
Systems which provide shadowing for imaged three-dimensional objects, about which three-dimensional information is available, are commercially available from companies such as Pixer, Softimage and Renderman.